The greater the heat capacity of
a material, the more heat energy it can hold for a given mass of material.
This means that high heat
capacity materials can store lots of energy when heated and can then release
a lot if cooled down. In other words, materials with a high specific heat
capacity are good for storing heat energy - a good material for a thermal
energy store.
Materials used in
heaters/heating systems, usually have a high specific heat capacity eg water
(SHC H2O = 4180 J/kgoC, very high) is used in central heating systems
and is easily pumped
around house to distribute lots of heat where needed, an excellent 'mobile'
thermal energy store.
Water is also used as a coolant in
car engines because it can absorb a lot of thermal energy for a given
temperature increase. The thermal energy store of the engine block is
reduced and the thermal energy store of the water increased. The thermal
energy in the water is then transferred to the surrounding air to
increase its thermal energy store via the radiator grill.
The good old fashioned hot water
bottle is a nice convenient thermal energy store to heat up the bed.
Concrete (SHC 750-960 J/kgoC,
quite high) is used in night storage heaters (using cheap night-time
electricity).
The greater the mass of concrete, the greater
its rise in temperature rise (safely!) the greater its capacity to store
thermal energy, to be later released into the house in daytime..
Oil-filled
heaters are used for a small scale heat storage (SHC oil = 900 J/kgoC, not
as good as water) but will convect in the oil radiator and steadily release
heat.
An archaeological note!
Prehistoric man learned thousands of
years ago that hot stone retained a lot of thermal energy.
The heat capacity of natural stone is
usually around 840 J/kgoC.
Large stones were heated in a fire and
dropped into stone line cooking troughs like the one shown below.
The heat from the thermal energy store of
the stone increases the thermal energy store of the cooler water, so boiling
the water and cooking food like meat placed in the water filled trough.
It may seem crude, but brass cooking pots
were something of a luxury item for many prehistoric people!
This stone cooking trough is by the
Bronze age stone circle (shown below) at Drombeg, Co. Cork, Ireland.
Several of them were constructed on this
site and fed and connected by a diverted spring stream.
They can be found all over Ireland and
the UK, and presumably on continental Europe.
Native American Indians also used the
same technique by dropping hot stones into a wooden bowl of food and water.
